A procedure in which the sample (liquid or gas) is fed continuously into the chromatographic bed. In frontal chromatography no additional mobile phase is used. Thus, the sample feed is continuously applied to the column and the sample components will displace each other in order of decreasing affinity for the chromatographic medium (this is called sample self-displacement). The least retained solute will be obtained in a pure form (i.e. depleted of the more strongly retained components) until the other solutes break through.